Electric vehicles are increasingly viewed as desirable successors to the internal combustion-engine vehicles currently used for personal and mass transportation. Such electric vehicles may be ‘pure’, battery-powered, electric motor driven electric vehicles with no on-board internal combustion engine, or hybrid-electric vehicles with a small on-board internal combustion engine which may be employed for battery charging. In either case, electrical power stored in a battery is delivered to a traction motor which propels the vehicle. For a given vehicle, the available range under exclusively electric power primarily depends on the capacity and capabilities of its high-voltage (traction) battery capacity. Thus every effort is made to fully utilize the battery capacity of electric or hybrid-electric vehicles subject to packaging, weight or cost constraints.
Electric vehicles intended for a mass market usually incorporate the electrical accessories and convenience features, lighting, adjustable mirrors, power windows and such found on counterpart internal combustion engine vehicles. Hence, in addition to their high-voltage battery, electric vehicles may also incorporate a low-voltage, nominally 12 volt battery, sized and adapted to operate these accessories and convenience features. In a hybrid electric vehicle, the low-voltage battery may also operate the starter for the on-board internal combustion engine.
Hence there is a need to manage electrical power usage in such vehicles to enable efficient energy usage and extend vehicle range. Further gains in range may be obtained by addition of on-vehicle means for recapturing or regenerating electrical energy, for example, regenerative braking.
Even so, the range of such electrically-powered vehicles remains less than their internal combustion-engine counterparts. There is, thus, an on-going interest in the application of yet additional approaches for extending vehicle range when operating electric or hybrid-electric vehicles under only electric power.